African-American women have a substantially higher prevalence of hypertension and suffer greater morbidity and mortality due to blood pressure elevation than White-American women. Much of this ethnic difference in blood pressure is due to increased obesity in African-American women. In contrast, young African-American and White-American girls have similar levels of obesity and blood pressure. The hemodynamic changes that occur with developing obesity and result in this ethnic difference in blood pressure have not been well characterized. Crosssectional studies of adolescents have shown that despite similar blood pressure levels, African-Americans have higher total peripheral resistance while Whites have higher cardiac output. Cross-sectional studies of adults show that obesity is associated with elevation of cardiac output. If such an obesity-related increase in cardiac output is superimposed on the underlying elevation of total peripheral resistance in African-American girls, these hemodynamic factors could be responsible for the developing ethnic divergence in blood pressure seen in late adolescence as African-American girls develop an increasing prevalence and severity of obesity. The proposed investigation is a prospective cohort study of 355 African-American and 315 White-American females from the NHLBl Growth and Health Study as these women progress from age 18-19 years to age 21-22 years. The study will include yearly measurement of anthropometrics, blood pressure, and echocardiographic determination of cardiac output and total peripheral resistance. In addition, factors which may relate to changes in cardiac output and total peripheral resistance, such as circulating blood volume (left ventricular end-diastolic volume), heart rate, left ventricular contractility, whole blood viscosity, and left ventricular mass and geometry will be measured. This investigation will provide important new knowledge regarding the longitudinal changes and interrelationships among the potential hemodynamic factors which define the association between developing obesity and blood pressure elevation. In the clinical setting where obesity is very difficult to prevent or treat, it is important to understand the mechanisms by which obesity results in elevated blood pressure. The results of this cohort study will provide the basis for rational and specific clinical strategies to interrupt the pathophysiologic process by which obesity leads to hypertension and places African-American women at particularly increased risk for cardiovascular disease morbidity and mortality.